I am adding subtitles to a video using:
ffmpeg -i \"imput.mp4\" -lavfi \"subtitles=subtitles.srt:force_style=\'OutlineColour=&H100000000,BorderStyle=3,Outlin
in fact you can also put some margin like "MarginV=20" in order to teweak position of subtitles
ffmpeg2 -y -i "C:\Users\input.mxf" -pix_fmt yuv422p -vcodec mpeg2video -non_linear_quant 1 -flags +ildct+ilme -top 1 -dc 10 -intra_vlc 1 -qmax 6 -lmin "1*QP2LAMBDA" -vtag xd5c -rc_max_vbv_use 1 -rc_min_vbv_use 1 -g 12 -b:v 50000k -minrate 50000k -maxrate 51000k -bufsize 8000k -color_primaries 1 -color_trc 1 -colorspace 1 -vf "subtitles=subtitles_file.mxf_Subtitle.srt:force_style='OutlineColour=&H80000000,BorderStyle=3,Outline=1,Shadow=0,MarginV=20" -acodec copy "output.mxf"